Mailing List flyrotary@lancaironline.net Message #54891
From: Dwayne Parkinson <dwayneparkinson@yahoo.com>
Subject: Re: [FlyRotary] Re: Cooling Inlets
Date: Thu, 5 May 2011 16:02:56 -0700 (PDT)
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
OK, here's my crazy scheme.  Use NACA ducts for the inlet and have cowl flaps for the outlet.  Unlike normal fixed NACA ducts, I'm hoping I can make them work like vents that open and close.  I've seen this on at least two Sonex planes except they use them for cabin air inlets, not cooling.  I don't know if changing the height of the opening in a NACA duct in relation to it's width messes with the aerodynamics, but I'm hoping it doesn't.  Assuming that's the case, my great big hopeful idea is that I can balance the intake and the outlet area so that the cowl flaps and NACA ducts work in unison to maintain a perfectly balanced air flow through the cooling system with just enough cooling drag to keep the temps where they need to be.   I'm trying to address the idea that I've got to design the intake and cooling drag so it handles taxiing on a 95 degree day but then continue to pay that drag penalty as I'm cruising along at 10,000 feet in zero degree air.

Dwayne



From: Ed Anderson <eanderson@carolina.rr.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Saturday, April 30, 2011 9:00 AM
Subject: [FlyRotary] Re: Cooling Inlets

I agree, Steve.  There is no question each part of the cooling system  is critical and the total results is no better than the weakest link. 
 
Most studies I have read indicates that after a certain size in inlet area (from 25-35% of core frontal area) - the outlet size becomes the determining factor and further increases in intake provide no additional benefit and can hurt by increasing cooling drag.  Adding such things as cowl flaps can reduce the pressure in the outlet region and promote more airflow and cooling but naturally at the cost of more drag.  But, then at higher speeds with plenty of dynamic pressure, you can retract the cowl flaps and reduce the drag.
 
NACA ducts have been made to work with radiator cores - no question about that.  The question is would a different approach have produced a "better" cooling system.  Again, I think it depends on your intended operating environment. 
 
For a high speed cruise environment, I would think cooling drag might be of more importance than say perhaps a few pounds of additional weight, on the other hand if you are flying an already draggy biplane for example, cooling drag is probably a very small part of your over all drag, but getting cooling with low airspeed might be the system driver.
 
Its all about compromises - space, weight, flow, drag, etc. - oh, yes! - and cooling of course {:>)  all matched to your constraints and operating environment.
 
Ed
 

Sent: Friday, April 29, 2011 8:48 PM
Subject: [FlyRotary] Re: Cooling Inlets

Hi Ed and Dwayne

I'm working on my inlet and outlet for Renesis powered Glasair SIIRG.
It seems whenever we turn our attention to air, it is not about inlets or outlets but pressure differentials and the whole system.
A great inlet is killed by a lousy outlet, and both made mute by inadequate diffusion.
Perhaps a NACA would work adequately given a system with good diffusion that SUCKED well.

Cheers
Steve Izett
Not flying, so maybe completely deluded. 
Continues to more than respect Tracy's thoughts and practices.

On 30/04/2011, at 7:26 AM, Ed Anderson wrote:

Dwayne
 
There is a NACA study on NACA ducts which in essence found that while they were excellent for feeding an intake (an duct with no internal resistance such as a heat exchanger core) such as an engine intake, that their performance suffered relative to other duct configurations - where you had a radiator core installed.  The reason appeared to be that the pressure build up before the core hindered the airflow into the duct and caused a lot of the air to flow around the opening. On the good side, they were relatively low drag ducts. 
 
Now that being said, several approaches have been found that seems to offset the problems.  One that comes to mind is the placement of vortex generators which guide more airflow into the ducts and the other one is the placement of the inlet in a high pressure area.  Folks have used them successfully for cooling - so long as sufficient airflow can be achieved through the duct the core doesn't care what kind of opening is used.
 
Ed
 
Edward L. Anderson
Anderson Electronic Enterprises LLC
305 Reefton Road
Weddington, NC 28104
http://www.andersonee.com
http://www.eicommander.com

Sent: Friday, April 29, 2011 5:05 PM
Subject: [FlyRotary] Re: Cooling Inlets

OK, I gotta ask.  Does anyone use NACA ducts for cooling inlets?  Why or why not?  


From: Tracy <rwstracy@gmail.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Fri, April 29, 2011 9:49:00 AM
Subject: [FlyRotary] Re: Cooling Inlets

Some questions:
Prior reading seemed to indicate that the oil cooler did ~1/3 of the cooling, implying a 2/1 ratio on air requirements. This setup seems to have a significantly higher percentage allocated to oil. Is this a byproduct of heat exchanger differences, or the less efficient heat transfer ability of oil, or....?

2nd, assuming similar inlet & diffuser efficiencies, could the inlet areas mentioned be reduced by roughly 1/3 with reasonable expectation of cooling a 2 rotor Renesis?

On the subject of exit area: Does either heat exchanger have an exit duct? The RV guys with really fast Lyc powered planes all have some variation of exit ducting to smoothly re-accelerate and redirect exit air parallel to & at or above the slipstream. Even the stock RV-8 has a rounded lip at the bottom of the firewall (which the really fast guys say is much too small a radius...). And there's always the near-mythical P-51 system...

Thanks,
Charlie

The inlets were originally closer to the 2 - 1 area ratio but many experiments (mostly failures) ended up with the current sizes.  I just don't have it in me to go back and un-do them all.  Also wish I had tried these inlets with my original oil cooler which had about 1/3 more core volume and much thicker.   Might have been able to do the oil cooling with less CFM airflow.   But, I don't think there is much penalty for having more than enough (but properly faired) inlet area and throttling the airflow with a cowl flap.

Yes, I do think both inlets could be scaled down in area for a 2 rotor.

Neither of my heat exchangers have exit ducts.  Just not enough room to do this in their current locations.

Tracy
  


On Thu, Apr 28, 2011 at 4:23 PM, Charlie England <ceengland@bellsouth.net> wrote:
On 4/28/2011 8:07 AM, Tracy wrote:
Finally got around to finishing my cooling inlets. (pictures attached)  Up until now they were simply round pipes sticking out of the cowl.   The pipes are still there but they have properly shaped bellmouths on them.   The shape and contours were derived from a NASA contractor report (NASA_CR3485) that you can find via Google.  Lots of math & formulas in it but I just copied the best performing inlet picture of the contour.   Apparently there is an optimum radius for the inner and outer lip of the inlet.   There was no change to the inlet diameters of 5.25" on water cooler and 4.75" on oil cooler.

The simple pipes performed adequately in level flight at moderate cruise settings even on hot days but oil temps would quickly hit redline at high power level flight and in climb.  

The significant change with the new inlet shape is that they appear to capture off-axis air flow  (like in climb and swirling flow  induced by prop at high power)  MUCH better than the simple pipes.    First flight test was on a 94 deg. F day and I could not get the oil temp above 200 degrees in a max power climb.    They may have gone higher if the air temperature remained constant but at 3500 fpm the rapidly decreasing OAT kept the temps well under redline (210 deg F).

I have an air pressure instrument reading the pressure in front of the oil cooler and was amazed at the pressure recovered from the prop wash.  At 130 MPH the pressure would almost double when the throttle was advanced to WOT.   That did not happen nearly as much with the simple pipes.   

These inlets ROCK!

Tracy Crook

Perfect timing for me; I need to decide whether to take a loss & sell my (RV-7)  James Lyc style cowl & replace it with James' rotary cowl, or just modify the existing cowl.

Some questions:
Prior reading seemed to indicate that the oil cooler did ~1/3 of the cooling, implying a 2/1 ratio on air requirements. This setup seems to have a significantly higher percentage allocated to oil. Is this a byproduct of heat exchanger differences, or the less efficient heat transfer ability of oil, or....?

2nd, assuming similar inlet & diffuser efficiencies, could the inlet areas mentioned be reduced by roughly 1/3 with reasonable expectation of cooling a 2 rotor Renesis?

On the subject of exit area: Does either heat exchanger have an exit duct? The RV guys with really fast Lyc powered planes all have some variation of exit ducting to smoothly re-accelerate and redirect exit air parallel to & at or above the slipstream. Even the stock RV-8 has a rounded lip at the bottom of the firewall (which the really fast guys say is much too small a radius...). And there's always the near-mythical P-51 system...

Thanks,

Charlie







The contents of this email are confidential and intended only for the named recipients of this e-mail. If you have received this e-mail in error, you are hereby notified that any use, reproduction, disclosure or distribution or the information contained in this e-mail is prohibited. Please notify the sender immediately and then delete/destroy the e-mail and any printed copies. All liability for viruses is excluded to the fullest extent of the law.


Subscribe (FEED) Subscribe (DIGEST) Subscribe (INDEX) Unsubscribe Mail to Listmaster